CN109980675B - Double-fed magnetic suspension vertical axis wind power generation system for flexible direct current transmission and control method thereof - Google Patents

Abstract

The invention discloses a doubly-fed magnetic levitation vertical axis wind power generation system for flexible direct current transmission and its control method. It adopts a permanent magnet synchronous generator and a disk motor with 1/3 rated power to jointly form a double-feed structure of the wind power system. The disk motor is a power control unit and suspension mechanism, which can flexibly control the suspension and friction damping of the fan rotating body. The main power output of the permanent magnet synchronous generator is a non-controlled mechanism, and the machine-side converter is adjusted from a fully controlled bridge to a non-controllable rectifier. Reduce the cost of the vertical axis power generation system; adopt four-point air gap tracking control and a cross-coupling controller that comprehensively considers synchronization performance to collaboratively complete the multi-degree-of-freedom suspension of the wind turbine; use rotor flux orientation to decouple the disc motor stator current, and adopt double closed loops Cascade control implements progressive tracking of the fan's optimized speed and rated speed; four-point damping is used to regulate friction torque, combined with the maximum torque compensation control of the disc motor, to strictly control the rated power output of the permanent magnet generator.

Description

Doubly-fed magnetic levitation vertical axis wind power generation system for flexible DC transmission and its control method

Technical field

The invention relates to a power generation system and a control method thereof, in particular to a doubly-fed magnetic levitation vertical axis wind power generation system for flexible DC transmission and a control method thereof, which belongs to the field of wind power.

Background technique

As the energy crisis and environmental pollution become increasingly serious, wind power generation, which is strictly non-polluting, has attracted increasing attention from countries around the world. my country has clearly upgraded wind power generation from supplementary energy to alternative energy. However, the average wind speed in most areas of my country is lower than 5-6m/s. Increasing the research on high-power low-wind speed wind turbine models and their control strategies is an effective way to promote the development of low-wind speed wind power and realize the true practical application of wind power. Vertical-axis wind turbines do not require the yaw device required for horizontal-axis wind turbines. They have the advantages of low starting wind speed and easy installation. Especially the introduction of magnetic bearing technology greatly reduces the starting resistance torque of wind turbines, making them very suitable for low-wind areas. of low wind wind farms. Taylor's University in Malaysia, the University of Nottingham and Manipal International University use permanent magnet arrays and stator cores to form passive suspension, reducing the starting wind speed to 2-3m/s; American Global Wind Energy Technology, Jiangsu University, Hong Kong Polytechnic University, etc. have successively The use of active and passive suspension bearings greatly reduces the starting wind speed of vertical axis wind turbines, but the power level is generally below 15kW. Inner Mongolia Solide Wind Power Company and Guangzhou Yatu New Energy Co., Ltd. have developed a MW-class vertical axis wind turbine using magnetic levitation bearings and multi-layer blade wind collection mechanisms. The starting wind speed is reduced to 3-3.5m/s, but there are The following problems: using a mechanical coupling device to complete the coupling between the generator and the wind turbine rotor, there are problems such as wind energy capture control lag, mechanical impact, and output power fluctuations; using a full-power machine-side converter to adjust the generator speed and transmission power, switching losses Large, high failure rate, little control freedom; the overturning moment caused by the height difference of the multi-layer fan wind collection system can easily lead to changes in the radial suspension displacement of the fan rotating body axis, resulting in large friction losses and high power generation costs, seriously affecting the high-power vertical Practical implementation and popularization of axial wind power generation.

Contents of the invention

The main purpose of the present invention is to provide a doubly-fed magnetic levitation vertical axis wind power generation system for flexible DC transmission with low kWh cost, simple control, high wind energy utilization rate and high power in view of the defects or deficiencies in the existing technology. .

In order to achieve the above objectives, the doubly-fed magnetic levitation vertical axis wind power generation system for flexible DC power transmission of the present invention includes: a wind turbine rotating body, a permanent magnet generator, a magnetic levitation disk motor, a main power converter, a capture converter, and a damping transformer. It is composed of a converter, a boost converter, a transmitter station converter, an air gap sensor and an encoder, etc., which jointly complete the four-point suspension of the wind turbine, the maximum capture of wind energy, the rated power control of the permanent magnet generator, the damping control of the wind turbine and the DC feedback. electricity into the grid.

The wind turbine rotating body is composed of fan blades, a permanent magnet generator rotor, a damping winding and a casing. It rotates to capture wind energy and drives the permanent magnet generator rotor to rotate and generate electricity; the permanent magnet generator is the main generator for wind power conversion. , its stator output is connected to the flexible DC bus through the main power converter, boost converter and terminal station converter, which captures energy from the rotating body of the wind turbine and converts it into electrical energy that is fed into the DC transmission line.

The main power converter is a three-phase non-controllable rectifier, which is connected to the stator of the permanent magnet generator to rectify the variable frequency alternating current output from the stator. The boost converter is a BOOST converter, which increases the power by three times. The output voltage of the non-controllable rectifier, the end-station converter is a BOOST converter, and the high-voltage output side is connected to the flexible DC transmission line to maintain a constant output voltage of the boost converter.

The magnetic levitation disc motor is an auxiliary power generation device for wind energy regulation, including a damping winding and a torque winding. The damping winding is a disc-shaped structure and is divided into four groups according to the principle of equal division. Each group of windings is respectively connected to a damping converter. , independently controls the current of each damping winding, generates different electromagnetic attractions between the damping winding and the torque winding, and regulates the suspended air gap and friction torque between the fan rotating body and the tower; the rated value of the disk motor torque winding The power is set to one-third of the rated power of the permanent magnet generator, and is coupled with the DC output of the capture converter and the non-controllable rectifier. The torque winding generates electromagnetic torque under the action of the damping winding excitation current to regulate the permanent magnet power generation. Maximum wind energy capture and rated power control; the damping converters are four H-bridge converters, corresponding to four damping windings, one end of which is connected to the damping winding, and the other end is connected to the output end of the non-controllable rectifier , based on the measurement information of four air gap sensors, the winding current is adjusted, and the four-point floating fan rotating body is suspended.

The four air gap sensors are evenly installed on the lower side of the disk motor torque winding to measure the air gap between the torque winding and the four symmetrically distributed damping windings; the encoder is installed on the upper end of the tower, and the rotating shaft and fan rotate. Body elastic connection, measuring the rotation speed and rotation angle of the rotating body, capturing the converter control of the disk motor torque winding, feedback speed and decoupling required rotation angle.

The control method of the above-mentioned doubly-fed maglev vertical axis wind power generation system for flexible DC transmission adopts the following steps:

Step 1. Four-point suspension of the fan rotating body: when the wind speed V _w reaches the starting wind speed V _in , first prepare for suspension and adjust the four damping converter output currents i _f (i), where i =1,2,3,4 , corresponding to the four damping windings, gradually increase the electromagnetic attraction force f _e (i) between the disk motor torque winding and the damping winding, until the sum of the four electromagnetic attraction forces f _e (1)+ f _e (2)+ f _e (3)+ f _e (4)= mg , mg is the weight of the fan rotating body; then the fan rotating body is started in suspension, and the four-point floating air gap reference δ _ref is set, and the four damping converters are measured according to the corresponding air gap sensors. Suspension air gap δ (i) , calculate the suspension air gap error e (i) of each damping winding respectively = δ _ref - δ (i), under the action of the proportional integral differential PID regulator, the main reference of the excitation current i _f0 ^* (i), and then based on the four suspended air gap errors e (i), calculate the synchronization error of the four suspended air gaps E (i)=2 e (i)- e (i+1)- e (i-1) , under the action of the proportional differential PD controller, the compensation current reference value i _f1 ^* (i) of the four-point suspension synchronization difference is obtained, and then the total reference value of the four damping winding excitation currents is given as i _f ^* (i) = i _f0 ^* (i)+ i _f1 ^* (i), send the four damping winding excitation current reference i _f ^* (i) to the corresponding damping converter to generate four-point suspended electromagnetic attraction f _e (i) with synchronization error compensation ), the fan rotating body is stably suspended at the floating air gap δ _ref . The fan rotating body starts to float without friction and begins to capture energy. At this time, the capturing converter, main power converter and boost converter are all out of control. state.

Step 2, maximum capture of wind energy: When the wind speed V _w is lower than the rated wind speed V _N , the wind turbine rotor is suspended and stabilized at four points under the action of the damping converter, and then enters the maximum capture of wind energy. First, the optimization is obtained based on the wind speed and vertical axis fan power curve. The rotation speed ω _opt is set to the rotation speed reference ω _ref . The capture converter decouples the disk motor output current into a torque current i q and an excitation current according to the rotor flux orientation according to the encoder’s measured speed ω and rotation angle _θ . i _d , then calculate the speed deviation e _{ω =} ω _opt - ω , and generate the torque current reference i _q ^* under the action of the PID controller, thereby regulating the electromagnetic torque T _d and output power P _d of the disk motor torque winding, The fan rotating body is stably controlled at the optimized speed ω _opt ; the permanent magnet generator rotor rotates at the optimized speed ω _opt under the joint action of the fan blades and the disk motor torque winding, and is induced in the stator winding of the permanent magnet generator. Three-phase current is generated, rectified by a non-controllable rectifier, boost converter and terminal station converter, and then fed into the flexible DC circuit.

Step 3, permanent magnet generator rated power control: when the wind speed V _w exceeds the rated wind speed V _N , at the same time, the electromagnetic torque of the disc motor T _d ≦ T _dmax ( δ _ref ), where T _dmax ( δ _ref ) is the disc motor The maximum electromagnetic torque under the rated suspension air gap δ _ref , the fan rotating body is stably suspended at four points under the action of the damping converter, and the capture converter is calculated based on the measured output power P _m and rated power P _N of the permanent magnet generator. The power deviation e _{P =} P _N - P _m , generates a torque current reference i _q ^* under the action of the PID controller, regulates the electromagnetic torque T _d and output power P _d of the disk motor torque winding, and compares T _d in real time and T _dmax ( δ _ref ), when T _d ≧ T _dmax ( δ _ref ), the suspension air gap reference δ _ref is gradually increased according to the △ δ _ref amplitude , and the damping converter adjusts according to the newly adjusted suspension air gap reference δ _ref , increase the current of the four damping windings and the electromagnetic suction force. As the suspension air gap δ increases, T _dmax ( δ ) gradually increases until it reaches the maximum electromagnetic torque T _dmax of the disk motor. At this time, the corresponding maximum suspension air gap is δ _max , the wind turbine rotating body completely lands on the wind turbine tower, and the rated power P _N output of the permanent magnet generator is strictly controlled.

Step _{4, fan damping control: When the wind speed Vw exceeds the rated wind speed VN, but is less than the cut-out wind speed Vout ,} and the suspended _air gap δ reaches δmax , _the fan damping is controlled by the damping converter and the disk motor damping. The windings jointly control the friction torque T _f between the wind turbine rotating body and the tower. The disc motor torque winding performs maximum torque compensation control of the disc motor under the action of the capture converter, and controls the strict rated power P of the permanent magnet generator. _N output, the damping converter calculates the real-time power deviation e _{P =} P _N - P _m based on the measured permanent magnet generator output power P _m and rated power P _N , and generates a total if ^* under the action of the PID _controller . , are sent to four damping converters as current references according to the principle of equal division, changing the four damping winding currents if (i) and electromagnetic attraction f e _{( i} ), thereby changing the friction torque T _f ; capturing the converter According to the T _f generated by the damping winding, the disk motor compensation torque T _c = T _dmax - T _f is calculated in real time. According to the direct torque control, the torque current reference i _q ^* is set to quickly compensate and absorb the excess fan power. The rated power output of the captured converter and permanent magnet generator is combined through the non-controllable rectifier, and the power is fed into the grid through the BOOST step-up transformer and the terminal station converter.

Step 5: When the wind speed is greater than the cut-out wind speed, that is, V _w > V _out , the fan blades feather, the system cuts out the protection, and enters the shutdown state.

The beneficial effects of the present invention are:

1) A double-feed mechanism is composed of a permanent magnet synchronous generator and a magnetic levitation disk motor with 1/3 rated power level. The main power output is the permanent magnet synchronous generator, and the disk motor serves as the power control unit and suspension actuator. , flexibly adjust the suspension and rotation damping of the fan rotating body to achieve low wind speed starting and frictionless wind energy capture.

2) As a power control unit, the disc motor has a relatively small rated power, which greatly improves the dynamic response speed and wind energy utilization of wind energy capture; the power control mechanism of the disc motor makes the permanent magnet synchronous generator machine-side converter The controllable full-bridge converter is adjusted to a non-controllable rectifier, which greatly reduces the cost and reliability of vertical axis wind power generation.

3) The four-point suspension mechanism of the wind turbine rotating body can flexibly control the suspension, which is beneficial to suppressing the overturning moment caused by wind speed fluctuations, ensuring stable suspension of the wind turbine rotating body with multiple degrees of freedom, enabling low wind speed or even light wind starting, and can also be used as a power generator. The generator generates electricity, increasing the total power of the wind turbine by 1/3, greatly improving the utilization rate of wind energy, and is especially suitable for weak wind wind farms.

Description of drawings

Figure 1 is a schematic structural diagram of a doubly-fed magnetic levitation vertical axis wind power generation system for flexible DC transmission according to the present invention.

Figure 2 is a schematic diagram of the four-point suspension division mechanism and suspension principle structure of the damping winding of the disk motor of the present invention.

Figure 3 is a working principle diagram of the doubly-fed magnetic levitation vertical axis wind power generation system for flexible DC transmission according to the present invention.

In the picture: 1-fan axial blades, 2-permanent magnet generator stator, 3-permanent magnet generator rotor, 4-tower, 5-damping winding, 6-fan radial blades, 7-torque winding , 8-fan rotating body, 9-main power converter, 10-capture converter, 11-boost converter, 12-sending terminal converter, 14-damping converter 4, 15,- Damping converter 1, 16-damping converter 3, 17-damping converter 2, 18-encoder, 19-air gap sensor, 20-damping winding 1, 21-damping winding 2, 22-damping winding 4 , 23-damping winding 3.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings.

As shown in Figures 1 and 2, the doubly-fed magnetic levitation vertical axis wind power generation system for flexible DC transmission of the present invention includes: a wind turbine rotating body 8, a permanent magnet generator (2, 3), and a magnetic levitation disk motor (5, 7 ), main power converter 9, capture converter 10, damping converter (14~17), boost converter 11 and end station converter 12, air gap sensor 19 and encoder 18, etc. , collaboratively complete the four-point suspension of the wind turbine, maximum capture of wind energy, rated power control of the permanent magnet generator, damping control of the wind turbine, and DC feed into the power grid.

The fan rotating body is composed of fan blades (1, 6), permanent magnet generator rotor 3, damping windings (20~23) and a casing. It rotates to capture wind energy and drives the permanent magnet generator rotor 3 to rotate and generate electricity; The permanent magnet generator is the main generator for wind power conversion. Its stator output is connected to the flexible DC bus through the main power converter 9, the boost converter 11 and the end station converter 12, and the wind turbine rotating body 8 captures energy. , converted into electrical energy and fed into the DC transmission line.

The main power converter 9 is a three-phase non-controllable rectifier, which is connected to the permanent magnet generator stator 2 and rectifies the variable frequency AC power output by the stator. The boost converter 11 is a BOOST converter. To increase the output voltage of the non-controllable rectifier by three times, the end-station converter 12 is a BOOST converter, and the high-voltage output side is connected to the flexible DC transmission line to maintain a constant output voltage of the boost converter.

The magnetic levitation disc motor is an auxiliary power generation device for wind energy regulation, including a damping winding (20~23) and a torque winding 7. The damping winding (20~23) is a disc-shaped structure and is divided into four groups according to the principle of equal division. Each set of windings is respectively connected to a damping converter (14~17), which independently controls the current of each damping winding, generates different electromagnetic suction forces between the damping windings and torque windings, and regulates the tension between the wind turbine rotating body 8 and the tower 4. Suspension air gap and friction torque; the rated power of the disk motor torque winding 7 is set to one third of the rated power of the permanent magnet generator, and is coupled with the DC output of the capture converter 10 and the non-controllable rectifier 9 , the torque winding 7 generates electromagnetic torque under the action of the damping winding excitation current, regulating the maximum capture of wind energy and rated power control of the permanent magnet generator; the damping converters (14~17) are four H-bridge converters , respectively corresponding to four damping windings (20~23), one end of which is connected to the damping winding, and the other end is connected to the output end of the non-controllable rectifier. According to the measurement information of the four air gap sensors, the winding current is adjusted, and the four-point suspension fan rotating body.

The four air gap sensors are evenly installed on the lower side of the disk motor torque winding to measure the air gap between the torque winding and the four symmetrically distributed damping windings; the encoder is installed on the upper end of the tower, and the rotating shaft and fan rotate. Body elastic connection, measuring the rotation speed and rotation angle of the rotating body, capturing the converter control of the disk motor torque winding, feedback speed and decoupling required rotation angle.

The control method of the above-mentioned doubly-fed maglev vertical axis wind power generation system for flexible DC transmission adopts the following steps:

Step 1. Four-point suspension of the fan rotating body: when the wind speed V _w reaches the starting wind speed V _in , first prepare for suspension and adjust the four damping converter output currents i _f (i), where i =1,2,3,4 , corresponding to the four damping windings, gradually increase the electromagnetic attraction force f _e (i) between the disk motor torque winding and the damping winding, until the sum of the four electromagnetic attraction forces f _e (1)+ f _e (2)+ f _e (3)+ f _e (4)= mg , mg is the weight of the fan rotating body; then the fan rotating body is started in suspension, and the four-point floating air gap reference δ _ref is set, and the four damping converters are measured according to the corresponding air gap sensors. Suspension air gap δ (i) , calculate the suspension air gap error e (i) of each damping winding respectively = δ _ref - δ (i), under the action of the proportional integral differential PID regulator, the main reference of the excitation current i _f0 ^* (i), and then based on the four suspended air gap errors e (i), calculate the synchronization error of the four suspended air gaps E (i)=2 e (i)- e (i+1)- e (i-1) , under the action of the proportional differential PD controller, the compensation current reference value i _f1 ^* (i) of the four-point suspension synchronization difference is obtained, and then the total reference value of the four damping winding excitation currents is given as i _f ^* (i) = i _f0 ^* (i)+ i _f1 ^* (i), send the four damping winding excitation current reference i _f ^* (i) to the corresponding damping converter to generate four-point suspended electromagnetic attraction f _e (i) with synchronization error compensation ), the fan rotating body is stably suspended at the floating air gap δ _ref . The fan rotating body starts to float without friction and begins to capture energy. At this time, the capturing converter, main power converter and boost converter are all out of control. state.

Step 2, maximum capture of wind energy: When the wind speed V _w is lower than the rated wind speed V _N , the wind turbine rotor is suspended and stabilized at four points under the action of the damping converter, and then enters the maximum capture of wind energy. First, the optimization is obtained based on the wind speed and vertical axis fan power curve. The rotation speed ω _opt is set to the rotation speed reference ω _ref . The capture converter decouples the disk motor output current into a torque current i q and an excitation current according to the rotor flux orientation according to the encoder’s measured speed ω and rotation angle _θ . i _d , then calculate the speed deviation e _{ω =} ω _opt - ω , and generate the torque current reference i _q ^* under the action of the PID controller, thereby regulating the electromagnetic torque T _d and output power P _d of the disk motor torque winding, The fan rotating body is stably controlled at the optimized speed ω _opt ; the permanent magnet generator rotor rotates at the optimized speed ω _opt under the joint action of the fan blades and the disk motor torque winding, and is induced in the stator winding of the permanent magnet generator. Three-phase current is generated, rectified by a non-controllable rectifier, boost converter and terminal station converter, and then fed into the flexible DC circuit.

Step 3, permanent magnet generator rated power control: when the wind speed V _w exceeds the rated wind speed V _N , at the same time, the electromagnetic torque of the disc motor T _d ≦ T _dmax ( δ _ref ), where T _dmax ( δ _ref ) is the disc motor The maximum electromagnetic torque under the rated suspension air gap δ _ref , the fan rotating body is stably suspended at four points under the action of the damping converter, and the capture converter is calculated based on the measured permanent magnet generator output power P _m and rated power P _N The power deviation e _{P =} P _N - P _m , generates a torque current reference i _q ^* under the action of the PID controller, regulates the electromagnetic torque T _d and output power P _d of the disk motor torque winding, and compares T _d in real time and T _dmax ( δ _ref ), when T _d ≧ T _dmax ( δ _ref ), the suspension air gap reference δ ref is gradually increased according to the amplitude of △ δ _ref , and the damping converter adjusts the suspension air gap reference δ _ref according to the new _adjustment . , increase the current of the four damping windings and the electromagnetic suction force. As the suspension air gap δ increases, T _dmax ( δ ) gradually increases until it reaches the maximum electromagnetic torque T _dmax of the disk motor. At this time, the corresponding maximum suspension air gap is δ _max , the wind turbine rotating body completely lands on the wind turbine tower, and the rated power P _N output of the permanent magnet generator is strictly controlled.

Step _{4, fan damping control: When the wind speed Vw exceeds the rated wind speed VN, but is less than the cut-out wind speed Vout ,} and the suspended _air gap δ reaches δmax , _the fan damping is controlled by the damping converter and the disk motor damping. The windings jointly control the friction torque T _f between the wind turbine rotating body and the tower. The disc motor torque winding performs maximum torque compensation control of the disc motor under the action of the capture converter, and controls the strict rated power P of the permanent magnet generator. _N output, the damping converter calculates the real-time power deviation e _{P =} P _N - P _m based on the measured permanent magnet generator output power P _m and rated power P _N , and generates a total if ^* under the action of the PID _controller . , are sent to four damping converters as current references according to the principle of equal division, changing the four damping winding currents if (i) and electromagnetic attraction f e _{( i} ), thereby changing the friction torque T _f ; capturing the converter According to the T _f generated by the damping winding, the disk motor compensation torque T _c = T _dmax - T _f is calculated in real time. According to the direct torque control, the torque current reference i _q ^* is set to quickly compensate and absorb the excess fan power via The rated power output of the captured converter and permanent magnet generator is combined through the non-controllable rectifier, and the power is fed into the grid through the BOOST step-up transformer and the terminal station converter.

Step 5: When the wind speed is greater than the cut-out wind speed, that is, V _w > V _out , the fan blades feather, the system cuts out the protection, and enters the shutdown state.

Claims (2)

1. A doubly-fed magnetic levitation vertical axis wind power generation system for flexible DC transmission, which is characterized by including a wind turbine rotating body, a permanent magnet generator, a magnetic levitation disk motor, a main power converter, a capture converter, and a damping transformer. It is composed of a converter, a boost converter, a transmitter station converter, an air gap sensor and an encoder. The permanent magnet generator is the main power output, and the magnetic levitation disk motor is the power control unit and suspension actuator. , together form a double feed mechanism, collaboratively completing the four-point suspension of the wind turbine, maximum wind energy capture, permanent magnet generator rated power control, wind turbine damping control and DC feed into the grid, achieving low wind speed starting and frictionless wind energy capture; the wind turbine The rotating body is composed of a fan blade, a permanent magnet generator rotor, a damping winding and a casing. The rotation captures wind energy and drives the permanent magnet generator rotor to rotate and generate electricity. The permanent magnet generator is the main generator for wind power conversion, and its stator The output is connected to the flexible DC bus through the main power converter, the boost converter and the terminal station converter, and the fan rotating body captures the energy and converts it into electrical energy that is fed into the DC transmission line; the main power converter It is a three-phase non-controllable rectifier, which is connected to the stator of the permanent magnet generator to rectify the variable frequency AC power output by the stator. The boost converter is a BOOST converter, which triples the output voltage of the non-controllable rectifier. , the end-station converter is a BOOST converter, and the high-voltage output side is connected to the flexible DC transmission line to maintain a constant output voltage of the boost converter; the magnetic levitation disk motor is a wind energy regulation auxiliary power generation device, including Damping winding and torque winding. The damping winding has a disk-shaped structure and is divided into four groups according to the principle of equal division. Each group of windings is respectively connected to the damping converter and independently controls the current of each damping winding. Between the damping winding and the torque Different electromagnetic attractions are generated between the windings to regulate the suspended air gap and friction torque between the fan rotating body and the tower; the rated power of the disk motor torque winding is set to one-third of the rated power of the permanent magnet generator , and coupled with the DC output of the capture converter and the non-controllable rectifier, the torque winding generates electromagnetic torque under the action of the damping winding excitation current, regulating the maximum wind energy capture and rated power control of the permanent magnet generator; the air gap sensor There are four, which are evenly installed on the lower side of the disk motor torque winding, and the air gap between the torque winding and the four symmetrically distributed damping windings is measured; the damping converter is four H-bridge converter, corresponding to Four damping windings, one end of which is connected to the damping winding and the other end to the output of the non-controllable rectifier, adjusts the winding current according to the measurement information of the four air gap sensors, and suspends the fan rotating body at four points; the encoder is installed At the upper end of the tower, the rotating shaft is elastically connected to the rotating body of the wind turbine, and the rotational speed and rotation angle of the rotating body are measured to capture the inverter control of the disk motor torque winding, feedback the rotational speed and the rotation angle required for decoupling. 2. A control method for a doubly-fed magnetic levitation vertical axis wind power generation system for flexible DC transmission as claimed in claim 1, characterized in that the following steps are adopted: Step 1. Four-point suspension of the fan rotating body: when the wind speed V _w reaches the starting wind speed V _in , first prepare for suspension and adjust the four damping converter output currents i _f (i), where i =1,2,3,4 , corresponding to the four damping windings, gradually increase the electromagnetic attraction force f _e (i) between the disk motor torque winding and the damping winding, until the sum of the four electromagnetic attraction forces f _e (1)+ f _e (2)+ f _e (3)+ f _e (4)= mg , mg is the weight of the fan rotating body; then the fan rotating body is started in suspension, and the four-point floating air gap reference δ _ref is set, and the four damping converters are measured according to the corresponding air gap sensors. Suspension air gap δ (i) , calculate the suspension air gap error e (i) of each damping winding respectively = δ _ref - δ (i), under the action of the proportional integral differential PID regulator, the main reference of the excitation current i _f0 ^* (i), and then based on the four suspended air gap errors e (i), calculate the synchronization error of the four suspended air gaps E (i)=2 e (i)- e (i+1)- e (i-1) , under the action of the proportional differential PD controller, the compensation current reference value i _f1 ^* (i) of the four-point suspension synchronization difference is obtained, and then the total reference value of the four damping winding excitation currents is given as i _f ^* (i) = i _f0 ^* (i)+ i _f1 ^* (i), send the four damping winding excitation current reference i _f ^* (i) to the corresponding damping converter to generate four-point suspended electromagnetic attraction f _e (i) with synchronization error compensation ), the fan rotating body is stably suspended at the floating air gap δ _ref . The fan rotating body starts to float without friction and begins to capture energy. At this time, the capturing converter, main power converter and boost converter are all out of control. state; Step 2, maximum capture of wind energy: When the wind speed V _w is lower than the rated wind speed V _N , the wind turbine rotor is suspended and stabilized at four points under the action of the damping converter, and then enters the maximum capture of wind energy. First, the optimization is obtained based on the wind speed and vertical axis fan power curve. The rotation speed ω _opt is set to the rotation speed reference ω _ref . The capture converter decouples the disk motor output current into a torque current i q and an excitation current according to the rotor flux orientation according to the encoder’s measured speed ω and rotation angle _θ . i _d , then calculate the speed deviation e _{ω =} ω _opt - ω , and generate the torque current reference i _q ^* under the action of the PID controller, thereby regulating the electromagnetic torque T _d and output power P _d of the disk motor torque winding, The fan rotating body is stably controlled at the optimized speed ω _opt ; the permanent magnet generator rotor rotates at the optimized speed ω _opt under the joint action of the fan blades and the disk motor torque winding, and is induced in the stator winding of the permanent magnet generator. Three-phase current is generated, rectified by the non-controllable rectifier, boost converter and terminal station converter, and fed into the flexible DC circuit; Step 3, permanent magnet generator rated power control: when the wind speed V _w exceeds the rated wind speed V _N , at the same time, the electromagnetic torque of the disc motor T _d ≦ T _dmax ( δ _ref ), where T _dmax ( δ _ref ) is the disc motor The maximum electromagnetic torque under the rated suspension air gap δ _ref , the fan rotating body is stably suspended at four points under the action of the damping converter, and the capture converter is calculated based on the measured output power P _m and rated power P _N of the permanent magnet generator. Power deviation e _{P =} P _N - P _m , the torque current reference i _q ^* is generated under the action of the PID controller, the electromagnetic torque T _d and output power P d of the disk motor torque winding are controlled, and T _d and output power P _d are compared in real time. T _dmax ( δ _ref ) relationship, when T _d ≧ T _dmax ( δ _ref ), the suspension air gap reference δ _ref is gradually increased according to the △ δ _ref amplitude , and the damping converter is based on the newly adjusted suspension air gap reference δ _ref . Increasing the four damping winding currents and electromagnetic suction, as the floating air gap δ increases, T _dmax ( δ ) gradually increases until it reaches the maximum electromagnetic torque T _dmax of the disk motor. At this time, the corresponding maximum floating air gap is δ _max , the wind turbine rotating body completely lands on the wind turbine tower, and the rated power P _N output of the permanent magnet generator is strictly controlled; Step _{4, fan damping control: When the wind speed Vw exceeds the rated wind speed VN, but is less than the cut-out wind speed Vout ,} and the suspended _air gap δ reaches δmax , _the fan damping is controlled by the damping converter and the disk motor damping. The windings jointly control the friction torque T _f between the wind turbine rotating body and the tower. The disc motor torque winding performs maximum torque compensation control of the disc motor under the action of the capture converter, and controls the strict rated power P of the permanent magnet generator. _N output, the damping converter calculates the real-time power deviation e _{P =} P _N - P _m based on the measured permanent magnet generator output power P _m and rated power P _N , and generates a total if ^* under the action of the PID _controller . , are sent to four damping converters as current references according to the principle of equal division, changing the four damping winding currents if (i) and electromagnetic attraction f e _{( i} ), thereby changing the friction torque T _f ; capturing the converter According to the T _f generated by the damping winding, the disk motor compensation torque T _c = T _dmax - T _f is calculated in real time. According to the direct torque control, the torque current reference i _q ^* is set to quickly compensate and absorb the excess fan power. The rated power output of the converter and the permanent magnet generator is captured through the non-controllable rectifier, and the power is fed into the grid through the BOOST step-up transformer and the terminal station converter; Step 5: When the wind speed is greater than the cut-out wind speed, that is, V _w > V _out , the fan blades feather, the system cuts out the protection, and enters the shutdown state.